(1) Field of the Invention
The present invention relates to apparatus for calcining gypsum and similar materials, and more particularly refers to an apparatus in which the heat applied for the calcining process is more efficiently utilized.
(2) Description of the Prior Art
Gypsum calcination may be carried out in either rotary kilns or in kettles. Either form of apparatus may be operated either continuously or batchwise.
In the process for calcining gypsum, gypsum in the form of calcium sulfate dihydrate is heated and converted to calcium sulfate hemi-hydrate, more commonly known as stucco or plaster. A large amount of heat is consumed in the calcining process. A portion of the heat is used to decompose the dihydrate crystals and transform them to the hemi-hydrate crystals. Additionally, a substantial amount of heat is utilized to drive off the water released in the calcining process. Various means are utilized for providing the necessary heat. In U.S. Pat. No. 3,901,645, a heating system is disclosed involving the use flat flame burners for heating the bottom wall of the kettle, and additionally a luminous wall furnace for heating the side wall of the kettle. However, when the heating means is applied solely to the walls of the kettle, the process is not as efficient as would be desirable. In U.S. Pat. No. 3,871,829, a horizontal calcining apparatus is shown as utilizing a gas flame for heating the horizontally disposed kettle. There again only the surface of the kettle imparts heat to the gypsum content being processed.
In U.S. Pat. No. 3,378,246, a vertical kettle type of calcining apparatus is disclosed utilizing a heating chamber through which hot gasses are passed for heating the kettle. However, here to, only the walls of the kettle transmit heat to the gypsum content inside also resulting in a somewhat decreased efficiency in terms of heat utilized.
Because of the present crisis due to the scarcity and high cost of fuel of various forms, it is highly desirable and important to develop a calcining apparatus which is more efficient in fuel utilization.